The present invention generally relates to the field of fluid sensors and more particularly to the field of portable fluid sensor devices and methods useful in field operations, including field operations involving process monitoring, process control and/or process or system servicing. The present invention relates, in preferred embodiments, to portable fluid sensor devices and methods adapted for use in closed fluid systems such as recirculating fluid systems (e.g., environmental control systems, engine systems, transportation vehicle systems, etc.). The present invention relates, in particularly preferred embodiments, to the field of fluid sensor devices and methods involving a mechanical resonator sensor such as a flexural resonator sensor.
Effective approaches for measuring characteristics of fluids using mechanical resonators are disclosed in commonly-owned U.S. Pat. Nos. 6,401,519; 6,393,895; 6,336,353; 6,182,499; and 6,494,079, each of which are incorporated by reference herein for all purposes. See also, Matsiev, “Application of Flexural Mechanical Resonators to Simultaneous Measurements of Liquid Density and Viscosity,” IEEE International Ultrasonics Symposium, Oct. 17-20, 1999, Lake Tahoe, Nev. and EP 0943091 B1. The use of a quartz oscillator in a sensor has been described as well in U.S. Pat. Nos. 6,223,589 and 5,741,961, and in Hammond, et al., “An Acoustic Automotive Engine Oil Quality Sensor”, Proceedings of the 1997 IEEE International Frequency Control Symposium, IEEE Catalog No. 97CH36016, pp. 72-80, May 28-30, 1997.
The use of other types of sensors is also known in the art. For example, the use of acoustic sensors has been addressed in applications such as viscosity measurement in J. W. Grate, et al, Anal. Chem. 65, 940A-948A (1993)); “Viscosity and Density Sensing with Ultrasonic Plate Waves”, B. A. Martin, S. W. Wenzel, and R. M. White, Sensors and Actuators, A21-A23 (1990), 704-708; “Preparation of chemically etched piezoelectric resonators for density meters and viscometers”, S. Trolier, Q. C. Xu, R. E. Newnham, Mat. Res. Bull. 22, 1267-74 (1987); “On-line Sensor for Density and Viscosity Measurement of a Liquid or Slurry for Process Control in the Food Industry”, Margaret S. Greenwood, Ph.D. James R. Skorpik, Judith Ann Bamberger, P. E. Sixth Conference on Food Engineering, 1999 AIChE Annual Meeting, Dallas, Tex.; U.S. Pat. Nos. 5,708,191; 5,886,250; 6,082,180; 6,082,181; and 6,311,549; and “Micromachined viscosity sensor for real-time polymerization monitoring.”, O. Brand, J. M. English, S. A. Bidstrup, M. G. Allen, Transducers '97, 121-124 (1997). See also, U.S. Pat. No. 5,586,445 (“Low Refrigerant Charge Detection Using a Combined Pressure/Temperature Sensor”).
Notwithstanding the above, there remains a need in the art for alternative or improved sensor devices and methods for efficiently evaluating fluids used in fluidic systems, including for example in residential, commercial and industrial process streams and/or in machines used in such process streams and/or in stand-alone machines. Examples in which such a need exists include those fluidic systems used in connection with the petroleum, chemical, pharmaceutical, healthcare, environmental, military, aerospace, construction, heating, ventilating, air-conditioning, refrigeration, food, and transportation industries. In particular, there remains a need in the art for a cost-effective, more universal flexural resonator sensing element that can be employed across a wide variety of fluids, including for example ionic fluids.